Deposition of pure metals in 3d structures

ABSTRACT

A system and method generate atomic hydrogen (H) for deposition of a pure metal in a three-dimensional (3D) structure. The method includes forming a monolayer of a compound that includes the pure metal. The method also includes depositing the monolayer on the 3D structure and immersing the 3D structure with the monolayer in an electrochemical cell chamber including an electrolyte. Applying a negative bias voltage to the 3D structure with the monolayer and a positive bias voltage to a counter electrode generates atomic hydrogen from the electrolyte and deposits the pure metal from the monolayer in the 3D structure.

BACKGROUND

The present invention relates to atomic layer deposition (ALD), and more specifically, to generating atomic hydrogen (H) for deposition of pure metals.

Atomic layer deposition (ALD) is a thin film deposition technique with applications in microelectronics. ALD may be used, for example, to deposit high permittivity gate oxides or capacitor dielectrics, ferroelectrics, and metals and nitrides for electrodes and interconnects. ALD of pure metals (e.g., Ti) requires atomic hydrogen (H). Typically, atomic H is generated using plasma. However, atomic H has a short lifetime and, therefore, recombines to H₂ before it can diffuse inside three-dimensional (3D) structures such as those of wafer substrates. As a result, the recombination prevents ALD deposition of pure metals in 3D structures. Another current approach involves generation of atomic H using thermal energy. However, this approach requires temperatures exceeding 1300 degrees Celsius. Such high temperatures are incompatible with complementary metal-oxide-semiconductor (CMOS) processing, because they approach the melting point of silicon (Si) and other front end of the line materials used in CMOS processing.

Consequently, a process to generate atomic H in a way that overcomes the above-noted issues with existing methods is sought by the microelectronics industry.

SUMMARY

According to an embodiment of the invention, a method of generating atomic hydrogen (H) for deposition of a pure metal in a three-dimensional structure (3D) includes forming a monolayer of a compound that includes the pure metal; depositing the monolayer on the 3D structure; immersing the 3D structure with the monolayer in an electrochemical cell chamber including an electrolyte; and applying a negative bias voltage to the 3D structure with the monolayer and a positive bias voltage to a counter electrode to generate atomic hydrogen from the electrolyte and deposit the pure metal from the monolayer in the 3D structure.

According to another embodiment of the invention, a system to deposit a pure metal in a three-dimensional (3D) structure includes an electrochemical cell comprising a soak chamber in which a monolayer of a compound including the pure metal is deposited on the 3D structure, and an electrolysis chamber in which atomic hydrogen (H) is generated at the 3D structure to facilitate deposition of the pure metal from the monolayer in the 3D structure.

Additional features and advantages are realized through the techniques of the present invention. Other embodiments and aspects of the invention are described in detail herein and are considered a part of the claimed invention. For a better understanding of the invention with the advantages and the features, refer to the description and to the drawings.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

The subject matter which is regarded as the invention is particularly pointed out and distinctly claimed in the claims at the conclusion of the specification. The forgoing and other features, and advantages of the invention are apparent from the following detailed description taken in conjunction with the accompanying drawings in which:

FIG. 1 depicts an apparatus to deposit a pure metal in a 3D structure prior to initiation of a deposition process according to an embodiment of the invention;

FIG. 2 depicts the apparatus of FIG. 1 during the deposition process according to an embodiment of the invention;

FIG. 3 depicts the apparatus of FIG. 1 during the deposition process according to an embodiment of the invention;

FIG. 4 depicts the apparatus of FIG. 1 during the deposition process according to an embodiment of the invention;

FIG. 5 depicts the apparatus of FIG. 1 at a completion of the deposition according to an embodiment of the invention;

FIG. 6 is a block diagram of a system to deposit a pure metal in a 3D structure according to an embodiment of the invention; and

FIG. 7 is a flow diagram illustrating an exemplary method of depositing a pure metal in a 3D structure according to an embodiment of the invention.

DETAILED DESCRIPTION

Embodiments detailed below describe a system and method to generate atomic hydrogen (H) on demand where it is needed for deposition of pure metals in three-dimensional (3D) structures. The detailed descriptions below are directed to the deposition of titanium (Ti) as an exemplary pure metal.

FIGS. 1-5 depict an apparatus 100 to deposit a pure metal in a 3D structure at various stages of deposition according to an embodiment. The exemplary 3D structures depicted in FIGS. 1-5 are part of the Si substrate of wafers 160. As the discussion of FIGS. 1-5 clarifies, the electrochemical generation of atomic hydrogen (H) may be performed at room temperature, and the arrangement positions the H where it is needed (before it recombines to H₂) in order to achieve metal deposition. As such, the apparatus 100 and accompanying method of pure metal deposition address the issues noted for previous H generation techniques.

FIG. 1 depicts the apparatus 100 which includes an electrochemical cell 110 with three chambers: a soak chamber 120, a buffer zone 130, and an electrolysis chamber 140. A compound including the pure metal to be deposited is introduced into the electrochemical cell 110 to form a monolayer. In the exemplary case, titanium tetrachloride (TiCl₄) 143 vapor with N₂ or Ar carrier gas 145 is injected into the soak chamber 120. In alternate embodiments, liquid TiCl₄ may be injected. The injection results in the formation of a monolayer of TiCl₄ in the soak chamber 120. A cassette of wafers 160 is stationed at a load port 170 of the buffer zone 130 in preparation for introduction into the buffer zone 130 which is filled with nitrogen. The cassette may include up to 25 wafers 160, for example. The number of wafers 160 in the cassette is based on the size of the chambers 120, 130, 140 that must accommodate the cassette of wafers 160 during the deposition process. An anode 150 is disposed in the electrolysis chamber 140. Surface pumps 180 are connected to each of the chambers 120, 130, 140.

FIG. 2 depicts the apparatus 100 with the cassette of wafers 160 transferred into the buffer zone 130 of the electrochemical cell 110 through the load port 170. In one embodiment, a mechanism 230 (FIG. 6) such as a robotic wafer handler may be used to execute the transfer so that an air break is not introduced in the electrochemical cell 110. In the electrolysis chamber 140, an electrolyte 210 may comprise HCl and H₂O with a pH of 3. FIG. 3 depicts the apparatus 100 with the cassette of wafers 160 moved to the soak chamber 120. In the soak chamber 120, each wafer 160 surface is coated with the monolayer of TiCl₄ 143. FIG. 4 depicts the cassette of wafers 160, now coated with the TiCl₄ 143 monolayer in the buffer chamber 130.

In FIG. 5, the cassette of wafers 160 coated with the TiCl₄ 143 monolayer is moved to the electrolysis chamber 140 and immersed (bathed in) the electrolyte 210. The electrolysis chamber 140 includes the counter electrode (anode 150). The anode 150 may be comprised of Ni or Pt, for example. A negative bias voltage 520 (−Ve) is applied to the wafers 160, and a positive bias voltage 530 (+Ve) is applied to the anode 150. The bias voltage value may be, for example, 1.48 V. The bias voltages 520, 530 may be generated from the same or different voltage sources 540. The application of the bias voltage generates H⁺. That is, the H₂O becomes H³⁰ and OH⁻. The H⁺ travels toward the wafers 160, which are negatively biased Si substrates with high aspect ratio 3D structures. While there, the H⁺ gains an electron to get reduced to H. This H is now readily available to reduce the monolayer of adsorbed TiCl₄ to produce pure metal (Ti) and HCl:

H⁺+e⁻→H   [EQ 1]

TiCl₄ (adsorbed monolayer)+H→Ti+HCl   [EQ 2]

The excess H recombines to form H₂. However, based on the arrangement of the apparatus 100 and, specifically, the availability of the H to the TiCl₄ monolayer, the excess H does not recombine before the pure metal (Ti) is deposited in the 3D structures of the wafers 160. At the anode 150, the OH⁻ ions would form O₂ as follows:

4OH⁻→O₂+2H₂O   [EQ 3]

The anode 150 is spatially separated and isolated from the wafers 160 such that the O₂ does not react with the deposited pure metal (Ti). The stages depicted by FIGS. 1-5 may be repeated, as needed, to complete the deposition process. A stage following the deposition of the pure metal (e.g., Ti) in the 3D structure of the wafers 160 involves rinsing the wafers using non-water-based aerosol or a methanol rinse to rinse off the excess electrolyte 210 from the wafers 160 after they emerge from the electrolysis chamber 140.

FIG. 6 is a block diagram of a system 200 to deposit a pure metal in a 3D structure according to an embodiment. The system 200 includes the apparatus 100, described with reference to FIGS. 1-5, that deposits a pure metal (e.g., Ti) in 3D structures of the wafers 160. The system 200 also includes one or more processors 210 and one or more memory devices 220. The processor 210 controls one or more aspects of deposition as shown in the various stages according to FIGS. 1-5. For example, the processor 210, in accordance with instructions stored in the memory device 220, controls one or more mechanisms 230, such as the robotic wafer handler that transfers the wafers 160 to the electrochemical cell 110. The processor 210 may also control the flow rate of TiCl₄ 143 vapor into the soak chamber 120. The mechanisms 230 may include the surface pumps, as well.

FIG. 7 is a flow diagram illustrating an exemplary method 300 of depositing a pure metal in a 3D structure. In the example discussed herein, the 3D structure is comprised in substrates of wafers 160 and TiCl₄ 143 is used to deposit a layer of pure metal Ti. At block 310, the processes 300 include forming a monolayer of compound including the pure metal to be deposited. For example, a TiCl₄ 143 monolayer is formed as discussed above with reference to FIG. 1. At block 320, transferring the 3D structure to the electrochemical cell 110 may include using a robotic wafer handler to transfer a cassette of wafers 160 into the electrochemical cell 110 through the load port 170, as discussed with reference to FIG. 2. At block 330, depositing the monolayer (e.g., TiCl₄ 143 monolayer) on the 3D structure (e.g., wafers 160) is done in the soak chamber 120 as discussed with reference to FIG. 3. Immersing the 3D structure in the electrochemical cell 110 chamber 140 including electrolyte 210 at block 340 may include immersing the cassette of wafers 160 into the electrolysis chamber 140 as discussed with reference to FIG. 5. At block 350, the method 300 includes applying a negative bias voltage 520 to the 3D structure (wafers 160) and a positive bias voltage to the anode 150 as shown in FIG. 5. As discussed with reference to FIG. 5, based on the voltage application in the electrolysis chamber 140, atomic H is generated and ALD of the pure metal (e.g., Ti) is completed. At block 360, after completion of the deposition, the method 300 may include rinsing excess electrolyte 210 from the wafers 160 and repeating the processes 300, as needed.

The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises” and/or “comprising,” when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one more other features, integers, steps, operations, element components, and/or groups thereof.

The description of the present invention has been presented for purposes of illustration and description, but is not intended to be exhaustive or limited to the invention in the form disclosed. Many modifications and variations will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the invention. The embodiment was chosen and described in order to best explain the principles of the invention and the practical application, and to enable others of ordinary skill in the art to understand the invention for various embodiments with various modifications as are suited to the particular use contemplated.

The flow diagram depicted herein is just one example. There may be many variations to this diagram or the steps (or operations) described therein without departing from the spirit of the invention. For instance, the steps may be performed in a differing order or steps may be added, deleted or modified. All of these variations are considered a part of the claimed invention.

While the preferred embodiment to the invention had been described, it will be understood that those skilled in the art, both now and in the future, may make various improvements and enhancements which fall within the scope of the claims which follow. These claims should be construed to maintain the proper protection for the invention first described. 

What is claimed is:
 1. A method of generating atomic hydrogen (H) for deposition of a pure metal in a three-dimensional (3D) structure, the method comprising: forming a monolayer of a compound that includes the pure metal; depositing the monolayer on the 3D structure; immersing the 3D structure with the monolayer in an electrochemical cell chamber including an electrolyte; and applying a negative bias voltage to the 3D structure with the monolayer and a positive bias voltage to a counter electrode to generate atomic hydrogen from the electrolyte and deposit the pure metal from the monolayer in the 3D structure.
 2. The method according to claim 1, wherein the forming the monolayer is performed in a soak chamber of an electrochemical cell.
 3. The method according to claim 2, wherein the forming the monolayer includes forming the monolayer of TiCl₄ by introducing TiCl₄ vapor with N₂ or Ar carrier gas into the soak chamber.
 4. The method according to claim 2, further comprising transferring the 3D structure to the electrochemical cell to perform the depositing the monolayer on the 3D structure.
 5. The method according to claim 1, wherein the immersing the 3D structure includes immersing the 3D structure in the electrolyte comprising H₂O and HCl.
 6. The method according to claim 5, wherein the applying the negative bias voltage to the 3D structure causes H³⁰ to move toward the 3D structure to form atomic H for the deposition of the pure metal from the monolayer.
 7. The method according to claim 1, wherein the 3D structure is a silicon wafer.
 8. A system to deposit a pure metal in a three-dimensional (3D) structure, the apparatus comprising: an electrochemical cell comprising a soak chamber in which a monolayer of a compound including the pure metal is deposited on the 3D structure, and an electrolysis chamber in which atomic hydrogen (H) is generated at the 3D structure to facilitate deposition of the pure metal from the monolayer in the 3D structure.
 9. The system according to claim 8, further comprising inlets in the soak chamber configured to take in TiCl₄ vapor with N₂ or Ar carrier gas to form the monolayer of TiCl₄.
 10. The system according to claim 8, further comprising a buffer zone between the soak chamber and the electrolysis chamber.
 11. The system according to claim 10, further comprising a robotic mechanism to transfer the 3D structure into the buffer zone of the electrochemical cell without introducing an air break.
 12. The system according to claim 11, further comprising surface pumps coupled to each of the soak chamber, the buffer zone, and the electrolysis chamber.
 13. The system according to claim 12, further comprising a controller configured to control at least one of the robotic mechanism or the surface pumps.
 14. The system according to claim 8, wherein the electrolysis chamber comprises an electrolyte including H₂O and HCl.
 15. The system according to claim 8, further comprising a voltage supply, wherein a negative bias voltage generated from the voltage supply is applied to the 3D structure and a positive bias voltage generated from the voltage supply is applied to a counter electrode in the electrolysis chamber to generate the H.
 16. The system according to claim 8, wherein the 3D structure is a silicon wafer. 